About 5,000 Nato and Afghan troops are engaged in a large offensive, Operation Achilles, in Helmand province in the south, the opium heartland of the world's biggest producer.
"Having security is of no use unless a massive amount of aid is invested into the community"
Justtone, Nottingham, UK
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British and Canadian troops make up the bulk of the International Security Assistance Force (Isaf) in the south of the country.
Canada's department of national defence said on Sunday that the six soldiers killed were Canadians.
Lieutenant Morgan Bailey, in Ottawa, said: "I can confirm they are Canadian but the identities have not been released. I don't have the specific details on the incident itself but they will be coming out shortly."
The latest deaths bring the Canadian toll to 51 since Ottawa sent troops to Afghanistan in 2002. Canada's main base is in the southern city of Kandahar.
Last year saw the bloodiest fighting in Afghanistan since the Taliban were ousted from power in 2001, mainly in the southern heartland of Helmand and neighbouring Kandahar province.
Britain has said it will send another 1,400 soldiers soon - making its deployment in Afghanistan greater than in Iraq. The United States has also committed an extra 3,200 soldiers.